Fix location-retention regression: stop GPS when backgrounded and idle

The previous fix (48ae3b0) dropped to ECONOMY (5 s interval) on app
pause, but never stopped location requests. The fusedLocationClient
continued polling indefinitely in the background even with nothing
recording or anchor-watching — accessing location without any need.

Fix:
- Add PowerMode.NONE to represent "no updates in flight"
- Add ACTION_STOP_UPDATES to LocationService: calls
  stopLocationUpdatesInternal() and parks _currentPowerMode at NONE
- Guard startLocationUpdatesInternal() against PowerMode.NONE so a
  stray setPowerMode(NONE) call can never request zero-interval updates
- Change _currentPowerMode initial value from FULL to NONE (accurate:
  no updates are running at process start)
- throttleLocationIfIdle() now sends ACTION_STOP_UPDATES instead of
  ACTION_START_ECONOMY; the existing restoreLocationMode() on onResume
  already sends ACTION_START_ECONOMY which transitions NONE→ECONOMY
  correctly since NONE != ECONOMY bypasses the no-op guard

Tracking and anchor-watch paths are unchanged: throttleLocationIfIdle()
skips the stop if either is active, and onResume sends ACTION_START_FULL
when recording is still in progress.

https://claude.ai/code/session_0126zvB69ccVoFtx2o96oaE2

3 files changed, 15 insertions, 8 deletions

diff --git a/android-app/app/src/main/kotlin/org/terst/nav/LocationService.kt b/android-app/app/src/main/kotlin/org/terst/nav/LocationService.kt
index c47c7a5..c1ff60e 100644
--- a/android-app/app/src/main/kotlin/org/terst/nav/LocationService.kt
+++ b/android-app/app/src/main/kotlin/org/terst/nav/LocationService.kt
@@ -270,6 +270,10 @@ class LocationService : Service() {
             }
             ACTION_START_ECONOMY -> setPowerMode(PowerMode.ECONOMY)
             ACTION_START_FULL    -> setPowerMode(PowerMode.FULL)
+            ACTION_STOP_UPDATES  -> serviceScope.launch {
+                stopLocationUpdatesInternal()
+                _currentPowerMode.emit(PowerMode.NONE)
+            }
             ACTION_START_ANCHOR_WATCH -> {
                 val radius = intent.getDoubleExtra(EXTRA_WATCH_RADIUS, AnchorWatchState.DEFAULT_WATCH_CIRCLE_RADIUS_METERS)
                 serviceScope.launch {
@@ -316,6 +320,7 @@ class LocationService : Service() {
 
     @SuppressLint("MissingPermission")
     private fun startLocationUpdatesInternal(powerMode: PowerMode) {
+        if (powerMode == PowerMode.NONE) return
         val priority = if (powerMode == PowerMode.FULL)
             Priority.PRIORITY_HIGH_ACCURACY
         else
@@ -411,8 +416,9 @@ class LocationService : Service() {
     companion object {
         const val ACTION_START_FOREGROUND_SERVICE = "ACTION_START_FOREGROUND_SERVICE"
         const val ACTION_STOP_FOREGROUND_SERVICE = "ACTION_STOP_FOREGROUND_SERVICE"
-        const val ACTION_START_ECONOMY = "ACTION_START_ECONOMY"
-        const val ACTION_START_FULL    = "ACTION_START_FULL"
+        const val ACTION_START_ECONOMY  = "ACTION_START_ECONOMY"
+        const val ACTION_START_FULL     = "ACTION_START_FULL"
+        const val ACTION_STOP_UPDATES   = "ACTION_STOP_UPDATES"
         const val ACTION_START_ANCHOR_WATCH = "ACTION_START_ANCHOR_WATCH"
         const val ACTION_STOP_ANCHOR_WATCH = "ACTION_STOP_ANCHOR_WATCH"
         const val ACTION_UPDATE_WATCH_RADIUS = "ACTION_UPDATE_WATCH_RADIUS"
@@ -469,7 +475,7 @@ class LocationService : Service() {
             _currentDirectionDeg.value = directionDeg
         }
 
-        private val _currentPowerMode = MutableStateFlow(PowerMode.FULL)
+        private val _currentPowerMode = MutableStateFlow(PowerMode.NONE)
         val currentPowerMode: StateFlow<PowerMode> get() = _currentPowerMode
 
         private val _tidalCurrentState = MutableStateFlow(TidalCurrentState())
diff --git a/android-app/app/src/main/kotlin/org/terst/nav/MainActivity.kt b/android-app/app/src/main/kotlin/org/terst/nav/MainActivity.kt
index 94b9c81..476fb0d 100644
--- a/android-app/app/src/main/kotlin/org/terst/nav/MainActivity.kt
+++ b/android-app/app/src/main/kotlin/org/terst/nav/MainActivity.kt
@@ -505,11 +505,11 @@ class MainActivity : AppCompatActivity(), SafetyFragment.SafetyListener {
     private fun locationServiceIntent(action: String) =
         Intent(this, LocationService::class.java).apply { this.action = action }
 
-    /** Drop to economy rate when the app goes to the background and nothing needs precision. */
+    /** Stop location updates when the app is backgrounded and nothing needs location. */
     private fun throttleLocationIfIdle() {
         if (!serviceStarted) return
         if (!viewModel.isRecording.value && !LocationService.anchorWatchState.value.isActive) {
-            startService(locationServiceIntent(LocationService.ACTION_START_ECONOMY))
+            startService(locationServiceIntent(LocationService.ACTION_STOP_UPDATES))
         }
     }
 
diff --git a/android-app/app/src/main/kotlin/org/terst/nav/PowerMode.kt b/android-app/app/src/main/kotlin/org/terst/nav/PowerMode.kt
index 22e1b77..d55c965 100644
--- a/android-app/app/src/main/kotlin/org/terst/nav/PowerMode.kt
+++ b/android-app/app/src/main/kotlin/org/terst/nav/PowerMode.kt
@@ -1,7 +1,8 @@
 package org.terst.nav
 
 enum class PowerMode(val gpsUpdateIntervalMillis: Long) {
-    FULL(1000L), // 1 Hz
-    ECONOMY(5000L), // 0.2 Hz
-    ANCHOR_WATCH(10000L) // 0.1 Hz
+    NONE(0L),          // no location updates (background idle)
+    FULL(1000L),       // 1 Hz, high accuracy
+    ECONOMY(5000L),    // 0.2 Hz, balanced accuracy
+    ANCHOR_WATCH(10000L) // 0.1 Hz, balanced accuracy
 }